The pneumatic tire has been the solution of choice for vehicular mobility for over a century. The pneumatic tire is a tensile structure. The pneumatic tire has at least four characteristics that make the pneumatic tire so dominant today. Pneumatic tires are efficient at carrying loads, because all of the tire structure is involved in carrying the load. Pneumatic tires are also desirable because they have low contact pressure, resulting in lower wear on roads due to the distribution of the load of the vehicle. Pneumatic tires also have low stiffness, which ensures a comfortable ride in a vehicle. The primary drawback to a pneumatic tire is that it requires compressed gasses. A conventional pneumatic tire is rendered useless after a complete loss of inflation pressure.
A tire designed to operate without inflation pressure may eliminate many of the problems and compromises associated with a pneumatic tire. Neither pressure maintenance nor pressure monitoring is required. Structurally supported tires such as solid tires or other elastomeric structures to date have not provided the levels of performance required from a conventional pneumatic tire. A structurally supported tire solution that delivers pneumatic tire-like performance would be a desirous improvement.
Non pneumatic tires are typically defined by their load carrying efficiency. “Bottom loaders” are essentially rigid structures that carry a majority of the load in the portion of the structure below the hub. “Top loaders” are designed so that all of the structure is involved in carrying the load. Top loaders thus have a higher load carrying efficiency than bottom loaders, allowing a design that has less mass.
The purpose of the shear band is to transfer the load from contact with the ground through tension in the spokes or connecting web to the hub 512, creating a top loading structure. When the shear band deforms, its preferred form of deformation is shear over bending. The shear mode of deformation occurs because of the inextensible membranes located on the outer portions of the shear band. Prior art non-pneumatic tire typically have a shear band made from rubber materials sandwiched between at least two layers of inextensible belts or membranes. The disadvantage to this type of construction is that the use of rubber significantly increases the cost and weight of the non-pneumatic tire. Another disadvantage to the use of rubber is that is generates heat, particularly in the shear band. Furthermore, the rubber in the shear band needs to be soft in shear, which makes it difficult to find the desired compound.
Thus an improved non-pneumatic tire is desired that has all the features of the pneumatic tires without the drawback of the need for air inflation is desired.